The present invention is related to the determination of temperature and temperature profile measurements in flowing polymer melts. More particularly, the present invention is related to non-contact means for determining temperature and temperature profiles within such melts using transmitted and reflected electromagnetic radiation in a selected wavelength range.
Precise measurement and control of polymer melt temperature in polymer processing is essential for ensuring the proper length of the polymer molecules and optimization of the physical properties of the final product. Traditionally, thermocouples have been used to obtain an indication of polymer melt temperature. Such measurements, however, are prone to errors due to several factors. First, frictional heating of the probe by the polymer melt flow itself can lead to erroneous temperature indications. Second, heat transfer from the heated conduit to the thermocouple can also contribute to erroneous temperature indications.
Recently, infrared detectors have been employed in a limited fashion to measure polymer surface temperatures. However, such infrared detectors have not been employed for determining the temperature and temperature profiles within the polymer melts. Their use has been confined to surface temperature measurements. See "Infrared Radiation Techniques for Glass Surface and Temperature Distribution Measurements", by R. Viskanta in the IEEE Trans. Indust., Appl. Vol. IA-11, No. 5 (1975).
It is thus seen that the use of thermocouples immersed in the polymer melt flow are not wholly satisfactory instruments for determining temperature because of the erroneous measurements arising from frictional heating of the thermocouples themselves. Additionally, such thermocouples generally exhibit a relatively slow response time. Moreover, surface temperature measurements performed on polymer melts using emitted radiation are limited because this measurement method is based on the fact that, at certain wavelengths, polymers behave like opaque materials. While this phenomena enables one to determine the temperature of a given surface by measuring the radiative intensity emitted from that surface, it nonetheless does not provide any means for determining interior temperatures which may, in fact, be more critical for ultimate material properties.
Accordingly, it is clear that the development of a method and apparatus capable of remote measurement of the internal temperature profile within a flowing polymer melt would be of great value to the polymer processing industry.